/******************************************************************************
 *
 * MantaFlow fluid solver framework
 * Copyright 2011 Tobias Pfaff, Nils Thuerey 
 *
 * This program is free software, distributed under the terms of the
 * Apache License, Version 2.0 
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Random numbers
 *
 * Based on an example by Makoto Matsumoto, Takuji Nishimura, Shawn Cokus, and Richard J. Wagner
 *
 ******************************************************************************/

#ifndef _RANDOMSTREAM_H
#define _RANDOMSTREAM_H 

#include <iostream>
#include <stdio.h>
#include <time.h>
#include "vectorbase.h"

namespace Manta {

class MTRand {
	// Data
	public:
		typedef unsigned long uint32;  // unsigned integer type, at least 32 bits

		enum { N = 624 };       // length of state vector
		enum { SAVE = N + 1 };  // length of array for save()

	protected:
		enum { M = 397 };  // period parameter

		uint32 state[N];   // internal state
		uint32 *pNext;     // next value to get from state
		int left;          // number of values left before reload needed


		//Methods
	public:
		MTRand( const uint32& oneSeed );  // initialize with a simple uint32
		MTRand( uint32 *const bigSeed, uint32 const seedLength = N );  // or an array
		MTRand();  // auto-initialize with /dev/urandom or time() and clock()

		// Do NOT use for CRYPTOGRAPHY without securely hashing several returned
		// values together, otherwise the generator state can be learned after
		// reading 624 consecutive values.

		// Access to 32-bit random numbers
		double rand();                          // real number in [0,1]
		double rand( const double& n );         // real number in [0,n]
		double randExc();                       // real number in [0,1)
		double randExc( const double& n );      // real number in [0,n)
		double randDblExc();                    // real number in (0,1)
		double randDblExc( const double& n );   // real number in (0,n)
		uint32 randInt();                       // integer in [0,2^32-1]
		uint32 randInt( const uint32& n );      // integer in [0,n] for n < 2^32
		double operator()() { return rand(); }  // same as rand()

		// Access to 53-bit random numbers (capacity of IEEE double precision)
		double rand53();  // real number in [0,1)

		// Access to nonuniform random number distributions
		double randNorm( const double& mean = 0.0, const double& variance = 1.0 );

		// Re-seeding functions with same behavior as initializers
		void seed( const uint32 oneSeed );
		void seed( uint32 *const bigSeed, const uint32 seedLength = N );
		void seed();

		// Saving and loading generator state
		void save( uint32* saveArray ) const;  // to array of size SAVE
		void load( uint32 *const loadArray );  // from such array
		friend std::ostream& operator<<( std::ostream& os, const MTRand& mtrand );
		friend std::istream& operator>>( std::istream& is, MTRand& mtrand );

	protected:
		void initialize( const uint32 oneSeed );
		void reload();
		uint32 hiBit( const uint32& u ) const { return u & 0x80000000UL; }
		uint32 loBit( const uint32& u ) const { return u & 0x00000001UL; }
		uint32 loBits( const uint32& u ) const { return u & 0x7fffffffUL; }
		uint32 mixBits( const uint32& u, const uint32& v ) const { 
			return hiBit(u) | loBits(v); 
		}
		uint32 twist( const uint32& m, const uint32& s0, const uint32& s1 ) const { 
			return m ^ (mixBits(s0,s1)>>1) ^ (-loBit(s1) & 0x9908b0dfUL); 
		}
		static uint32 hash( time_t t, clock_t c );
};


inline MTRand::MTRand( const uint32& oneSeed )
	{ seed(oneSeed); }

inline MTRand::MTRand( uint32 *const bigSeed, const uint32 seedLength )
	{ seed(bigSeed,seedLength); }

inline MTRand::MTRand()
	{ seed(); }

inline double MTRand::rand()
	{ return double(randInt()) * (1.0/4294967295.0); }

inline double MTRand::rand( const double& n )
	{ return rand() * n; }

inline double MTRand::randExc()
	{ return double(randInt()) * (1.0/4294967296.0); }

inline double MTRand::randExc( const double& n )
	{ return randExc() * n; }

inline double MTRand::randDblExc()
	{ return ( double(randInt()) + 0.5 ) * (1.0/4294967296.0); }

inline double MTRand::randDblExc( const double& n )
	{ return randDblExc() * n; }

inline double MTRand::rand53()
{
	uint32 a = randInt() >> 5, b = randInt() >> 6;
	return ( a * 67108864.0 + b ) * (1.0/9007199254740992.0);  // by Isaku Wada
}

inline double MTRand::randNorm( const double& mean, const double& variance )
{
	// Return a real number from a normal (Gaussian) distribution with given
	// mean and variance by Box-Muller method
	double r = sqrt( -2.0 * log( 1.0-randDblExc()) ) * variance;
	double phi = 2.0 * 3.14159265358979323846264338328 * randExc();
	return mean + r * cos(phi);
}

inline MTRand::uint32 MTRand::randInt()
{
	// Pull a 32-bit integer from the generator state
	// Every other access function simply transforms the numbers extracted here
	
	if( left == 0 ) reload();
	--left;
		
	uint32 s1;
	s1 = *pNext++;
	s1 ^= (s1 >> 11);
	s1 ^= (s1 <<  7) & 0x9d2c5680UL;
	s1 ^= (s1 << 15) & 0xefc60000UL;
	return ( s1 ^ (s1 >> 18) );
}

inline MTRand::uint32 MTRand::randInt( const uint32& n )
{
	// Find which bits are used in n
	// Optimized by Magnus Jonsson (magnus@smartelectronix.com)
	uint32 used = n;
	used |= used >> 1;
	used |= used >> 2;
	used |= used >> 4;
	used |= used >> 8;
	used |= used >> 16;
	
	// Draw numbers until one is found in [0,n]
	uint32 i;
	do
		i = randInt() & used;  // toss unused bits to shorten search
	while( i > n );
	return i;
}


inline void MTRand::seed( const uint32 oneSeed )
{
	// Seed the generator with a simple uint32
	initialize(oneSeed);
	reload();
}


inline void MTRand::seed( uint32 *const bigSeed, const uint32 seedLength )
{
	// Seed the generator with an array of uint32's
	// There are 2^19937-1 possible initial states.  This function allows
	// all of those to be accessed by providing at least 19937 bits (with a
	// default seed length of N = 624 uint32's).  Any bits above the lower 32
	// in each element are discarded.
	// Just call seed() if you want to get array from /dev/urandom
	initialize(19650218UL);
	const unsigned int Nenum = N;
	int i = 1;
	uint32 j = 0;
	int k = ( Nenum > seedLength ? Nenum : seedLength );
	for( ; k; --k )
	{
		state[i] =
			state[i] ^ ( (state[i-1] ^ (state[i-1] >> 30)) * 1664525UL );
		state[i] += ( bigSeed[j] & 0xffffffffUL ) + j;
		state[i] &= 0xffffffffUL;
		++i;  ++j;
		if( i >= N ) { state[0] = state[N-1];  i = 1; }
		if( j >= seedLength ) j = 0;
	}
	for( k = N - 1; k; --k )
	{
		state[i] =
			state[i] ^ ( (state[i-1] ^ (state[i-1] >> 30)) * 1566083941UL );
		state[i] -= i;
		state[i] &= 0xffffffffUL;
		++i;
		if( i >= N ) { state[0] = state[N-1];  i = 1; }
	}
	state[0] = 0x80000000UL;  // MSB is 1, assuring non-zero initial array
	reload();
}


inline void MTRand::seed()
{
	// Seed the generator with an array from /dev/urandom if available
	// Otherwise use a hash of time() and clock() values
	
	// First try getting an array from /dev/urandom
	FILE* urandom = fopen( "/dev/urandom", "rb" );
	if( urandom )
	{
		uint32 bigSeed[N];
		uint32 *s = bigSeed;
		int i = N;
		bool success = true;
		while( success && i-- )
			success = fread( s++, sizeof(uint32), 1, urandom );
		fclose(urandom);
		if( success ) { seed( bigSeed, N );  return; }
	}
	
	// Was not successful, so use time() and clock() instead
	seed( hash( time(NULL), clock() ) );
}


inline void MTRand::initialize( const uint32 intseed )
{
	// Initialize generator state with seed
	// See Knuth TAOCP Vol 2, 3rd Ed, p.106 for multiplier.
	// In previous versions, most significant bits (MSBs) of the seed affect
	// only MSBs of the state array.  Modified 9 Jan 2002 by Makoto Matsumoto.
	uint32 *s = state;
	uint32 *r = state;
	int i = 1;
	*s++ = intseed & 0xffffffffUL;
	for( ; i < N; ++i )
	{
		*s++ = ( 1812433253UL * ( *r ^ (*r >> 30) ) + i ) & 0xffffffffUL;
		r++;
	}
}


inline void MTRand::reload()
{
	// Generate N new values in state
	// Made clearer and faster by Matthew Bellew (matthew.bellew@home.com)
	uint32 *p = state;
	int i;
	for( i = N - M; i--; ++p )
		*p = twist( p[M], p[0], p[1] );
	for( i = M; --i; ++p )
		*p = twist( p[M-N], p[0], p[1] );
	*p = twist( p[M-N], p[0], state[0] );

	left = N, pNext = state;
}


inline MTRand::uint32 MTRand::hash( time_t t, clock_t c )
{
	// Get a uint32 from t and c
	// Better than uint32(x) in case x is floating point in [0,1]
	// Based on code by Lawrence Kirby (fred@genesis.demon.co.uk)

	static uint32 differ = 0;  // guarantee time-based seeds will change

	uint32 h1 = 0;
	unsigned char *p = (unsigned char *) &t;
	for( size_t i = 0; i < sizeof(t); ++i )
	{
		h1 *= std::numeric_limits<unsigned char>::max() + 2U;
		h1 += p[i];
	}
	uint32 h2 = 0;
	p = (unsigned char *) &c;
	for( size_t j = 0; j < sizeof(c); ++j )
	{
		h2 *= std::numeric_limits<unsigned char>::max() + 2U;
		h2 += p[j];
	}
	return ( h1 + differ++ ) ^ h2;
}


inline void MTRand::save( uint32* saveArray ) const
{
	uint32 *sa = saveArray;
	const uint32 *s = state;
	int i = N;
	for( ; i--; *sa++ = *s++ ) {}
	*sa = left;
}


inline void MTRand::load( uint32 *const loadArray )
{
	uint32 *s = state;
	uint32 *la = loadArray;
	int i = N;
	for( ; i--; *s++ = *la++ ) {}
	left = *la;
	pNext = &state[N-left];
}


inline std::ostream& operator<<( std::ostream& os, const MTRand& mtrand )
{
	const MTRand::uint32 *s = mtrand.state;
	int i = mtrand.N;
	for( ; i--; os << *s++ << "\t" ) {}
	return os << mtrand.left;
}


inline std::istream& operator>>( std::istream& is, MTRand& mtrand )
{
	MTRand::uint32 *s = mtrand.state;
	int i = mtrand.N;
	for( ; i--; is >> *s++ ) {}
	is >> mtrand.left;
	mtrand.pNext = &mtrand.state[mtrand.N-mtrand.left];
	return is;
}

// simple interface to mersenne twister
class RandomStream
{
public:
	inline RandomStream(long seed) : mtr(seed) {} ;
	~RandomStream() {}

	/*! get a random number from the stream */
	inline double getDouble( void ) { return mtr.rand(); };
	inline float  getFloat ( void ) { return (float)mtr.rand(); };

	inline float  getFloat( float min, float max ) { return mtr.rand(max-min) + min; };
	inline float  getRandNorm( float mean, float var) { return mtr.randNorm(mean, var); };

	#if FLOATINGPOINT_PRECISION==1
	inline Real getReal()           { return getFloat(); }

	#else
	inline Real getReal()           { return getDouble(); }
	#endif

	inline Vec3   getVec3 ()        { Real a=getReal(), b=getReal(), c=getReal(); return Vec3(a,b,c); }
	inline Vec3   getVec3Norm ()    { Vec3 a=getVec3(); normalize(a); return a; }

private: 
	MTRand mtr; 
};


} // namespace

#endif
